Core PHP Programming, Third Edition

27.4. Modularization Using include

Despite its name, the include function is not equivalent to C's preprocessor command of the same name. In many ways it is like a function call. Given the name of a file, PHP attempts to parse the file as if it appeared in place of the call to include. The difference from a function is that the code will be parsed only if the include statement is executed. You can take advantage of this by wrapping calls to include in if statements. The require function, however, will always include the specified file, even if it is inside an if block that is never executed. It has been discussed several times on the PHP mailing list that require is faster than include because PHP is able to inject the specified file into the ...